The present invention relates to an output buffer circuit, and more particularly relates to an output buffer circuit well adapted for use in a semiconductor integrated circuit to reduce noise.
It is generally required for an output buffer circuit incorporated in a semiconductor integrated circuit to be able to drive a load of a large capacity, which is connected to the output terminal of the circuit, at a high speed. High speed driving by an output buffer circuit of a high current drive capability, however, causes abrupt flow of a large current in the power source and earth lines at the moment of charge-up or discharge, thereby inducing undesirable noises in these lines. In particular in the case of a semiconductor integrated circuit, generation of such noises causes a serious problem since its input signal level and output voltage discrimination level are both close to the earth level.
It is proposed in Japanese Laid-open Patent No. 60-62725 to interpose a Miller capacitance between the input and output terminals of an output inverter circuit in an attempt to suppress generation of such undesirable noises.
The output buffer circuit of this earlier proposal is, however, quite unsuited for high speed operation since the Miller capacitance included therein slows the rise and fall of a signal wave form.